The present invention relates to data storage systems, and more particularly, this invention relates to mitigation of motor-induced disturbances applied to a tape reel.
In magnetic storage systems, magnetic transducers read data from and write data onto magnetic recording media. Data is written on the magnetic recording media by moving a magnetic recording transducer to a position over the media where the data is to be stored. The magnetic recording transducer then generates a magnetic field, which encodes the data into the magnetic media. Data is read from the media by similarly positioning the magnetic read transducer and then sensing the magnetic field of the magnetic media. Read and write operations may be independently synchronized with the movement of the media to ensure that the data can be read from and written to the desired location on the media.
An important and continuing goal in the data storage industry is that of increasing the density of data stored on a medium. For tape storage systems, that goal has led to increasing the track and linear bit density on recording tape, and decreasing the thickness of the recording tape medium. However, the development of small footprint, higher performance tape drive systems has created various problems in the design of a tape head assembly for use in such systems.
In a tape drive system, the drive moves the recording tape over the surface of the tape head at high speed. Usually the tape head is designed to minimize the spacing between the head and the tape. The spacing between the magnetic head and the recording tape is crucial and so goals in these systems are to have the recording gaps of the transducers, which are the source of the magnetic recording flux in near contact with the tape to effect writing sharp transitions, and to have the read elements in near contact with the tape to provide effective coupling of the magnetic field from the tape to the read elements.
For modern tape drive design, and magnetic recording tape design, it is useful to achieve as high of a storage capacity as physically possible. One way to achieve a relatively high storage capacity is via increasing track density, e.g., by writing narrower tracks. One way to enable use of a relatively higher track density is by improving (decreasing) the position error signal (PES) during writing, which is a measure of how far the actual tape head position is from a known position relative to the tape, and is typically provided by a track following system such as a timing-based servo track following system. Thus, the accuracy of PES-based positioning is reflected in the written tracks, and therefore PES errors cause the actual track placement to be offset from the desired track placement. Various mechanical and/or servo related efforts have been used in the past, attempting to improve PES within tape drives; however, the demand for increased storage capacities remains ongoing.
One source of PES-related problems in tape drive environments is disturbances originating from the reels and/or motors coupled to such reels. These disturbances can originate from events including (but not limited to) run-out, impacts of the tape and the reel flanges, electromechanical disturbances from the commutation of the reel motor itself, etc. One strategy that has been undertaken to mitigate the negative effects associated with these disturbances includes designing a variable frequency notch filter that can track the time-varying frequency of the reel motor. However, this strategy can cause increased error amplifications at other frequencies due to Bode's integral theorem.